These Crutches can be made from regular Crutches, and a section of Aluminium Tube.
You can make a pair of these in half an hour.
I hope to make a more step-by-stepish Instructable, soon, with the help of some Fab-Lab... ;)
You just need a Tube Cutting tool, a Riveter, an extra Aluminium Tube, a pair of rivets, and a rubber band, or whatever to keep the thing together, when folded.
This is all you need to make a pair of fold-able Crutches that are affordable, and you can trust, since this uses the same set-up as the height regulation, two holes in witch a pair of holding pins with a spring will snap onto.
Not shown above is the separate tube section, that is there, but already riveted.